irqchip/gic-v5: Enable GICv5 SMP booting

Set up IPIs by allocating IPI IRQs for all cpus and call into
arm64 core code to initialise IPIs IRQ descriptors and
request the related IRQ.

Implement hotplug callback to enable interrupts on a cpu
and register the cpu with an IRS.

Co-developed-by: Sascha Bischoff <sascha.bischoff@arm.com>
Signed-off-by: Sascha Bischoff <sascha.bischoff@arm.com>
Co-developed-by: Timothy Hayes <timothy.hayes@arm.com>
Signed-off-by: Timothy Hayes <timothy.hayes@arm.com>
Signed-off-by: Lorenzo Pieralisi <lpieralisi@kernel.org>
Reviewed-by: Marc Zyngier <maz@kernel.org>
Cc: Thomas Gleixner <tglx@linutronix.de>
Cc: Marc Zyngier <maz@kernel.org>
Link: https://lore.kernel.org/r/20250703-gicv5-host-v7-23-12e71f1b3528@kernel.org
Signed-off-by: Marc Zyngier <maz@kernel.org>

Author: Lorenzo Pieralisi

drivers/irqchip/irq-gic-v5.c

@@ -5,6 +5,7 @@
 
 #define pr_fmt(fmt)	"GICv5: " fmt
 
+#include <linux/cpuhotplug.h>
 #include <linux/idr.h>
 #include <linux/irqdomain.h>
 #include <linux/slab.h>
@@ -918,6 +919,8 @@ static void gicv5_cpu_enable_interrupts(void)
 	write_sysreg_s(cr0, SYS_ICC_CR0_EL1);
 }
 
+static int base_ipi_virq;
+
 static int gicv5_starting_cpu(unsigned int cpu)
 {
 	if (WARN(!gicv5_cpuif_has_gcie(),
@@ -929,6 +932,22 @@ static int gicv5_starting_cpu(unsigned int cpu)
 	return gicv5_irs_register_cpu(cpu);
 }
 
+static void __init gicv5_smp_init(void)
+{
+	unsigned int num_ipis = GICV5_IPIS_PER_CPU * nr_cpu_ids;
+
+	cpuhp_setup_state_nocalls(CPUHP_AP_IRQ_GIC_STARTING,
+				  "irqchip/arm/gicv5:starting",
+				  gicv5_starting_cpu, NULL);
+
+	base_ipi_virq = irq_domain_alloc_irqs(gicv5_global_data.ipi_domain,
+					      num_ipis, NUMA_NO_NODE, NULL);
+	if (WARN(base_ipi_virq <= 0, "IPI IRQ allocation was not successful"))
+		return;
+
+	set_smp_ipi_range_percpu(base_ipi_virq, GICV5_IPIS_PER_CPU, nr_cpu_ids);
+}
+
 static void __init gicv5_free_domains(void)
 {
 	if (gicv5_global_data.ppi_domain)
@@ -1050,6 +1069,8 @@ static int __init gicv5_of_init(struct device_node *node, struct device_node *pa
 	if (ret)
 		goto out_int;
 
+	gicv5_smp_init();
+
 	return 0;
 
 out_int: